In a die casting machine, a molten metal material (metal melt) such as an Al alloy or a Mg alloy melted in a melting furnace is measured and scooped every shot by a ladle. The scooped metal melt is poured into an injection sleeve. The metal melt is then injected/filled into a cavity of a mold in accordance with forward movement of an injection plunger. Thus, a product is obtained.
The casting procedure of the die casting machine includes an injection step consisting of a low-speed injection step and a high-speed injection step following the low-speed injection step, and a pressure intensification step following the high-speed injection step. The high-speed injection step requires a higher injection speed than that of injection molding of a plastic material. In addition, the pressure intensification step requires a higher boosting force than that of injection molding of a plastic material. Accordingly, a comparatively large-scale hydraulic drive source is heretofore generally used as a drive source for injection/pressure boosting. In addition, since the comparatively large-scale hydraulic drive source is provided, the hydraulic drive sources are often used as drive sources for opening/closing a mold or extruding a cast product.
However, such a hydraulic die casting machine is apt to contaminate a factory with oil. Therefore, there is an increasing request for an electric die casting machine to keep a factory clean. In order to cope with such a request, the present applicant has already proposed a die casting machine including a crank mechanism in which a first arm is rotationally driven by an electric servomotor and an injection plunger is rotatably linked with a front end of a second arm one end of which is rotatably linked with the first arm (see Patent Document 1). In this die casting machine, the crank mechanism is set in advance so that the high-speed injection step can be carried out in a rotational angle range where the relative speed of the injection plunger is the highest, and the pressure intensification step can be carried out in a rotational angle range where the magnifying ratio of force acting on the injection plunger is the highest. Thus, products can be cast without use of any hydraulic drive source.
Patent Document 1: JP-A-2008-114246